Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
An electronic image sensor can be formed of a pixelated array of photo-sensitive elements. The photo-sensitive elements can operate to detect incoming light via photodiodes in each element, which can be implemented in a silicon plane. Read out circuitry can be constructed from one or more thin film transistors (TFTs) associated with each photo-sensitive element. For example, a voltage corresponding to the light incident on the photodiode can be read out for each photo-sensitive element in the array. The resulting data from the pixelated array can then be used to determine a digital image representing the incoming light. Such an image sensor can be implemented using semiconductor assembly technologies, such as complementary metal-oxide-semiconductor (CMOS) technology. Such a CMOS array can be fabricated on a silicon wafer using patterned photodiodes and TFTs to provide a voltage output corresponding to the incident light. The voltage output can then be converted to a digital value and further analyzed/stored. Combining the digital values corresponding to incident light across an array of such CMOS sensors results in a digital representation of an image.
The semiconductor region of photodiodes is thus the photo-sensitive layer of an electronic image sensor. To focus incident light on the photo-sensitive layer, a primary lens typically focuses light passing through an aperture on a focal plane coincident with the photo-sensitive layer of the image sensor. The distance from the aperture to the focal plane is the focal length. The ratio between the focal length and the aperture diameter is the focal ratio or f-stop. Typical electronic image sensors include primary lenses with a thickness of at least several millimeters and also have a typical focal length of several millimeters. As a result, electronic image sensors generally have a form factor between the primary aperture lens and photo-sensitive layer of at least roughly 10 millimeters.